Recently, in the production of the base body of printed wiring boards that are used for electronic equipment such as personal computers, etc., the plating method that is called through hole plating or via fill plating, has been used. The speed of deposition of the plate film in the electrolytic copper plating is fast, 10 to 50 μm/hr, therefore, the application of this for through hole and via fill plating has been expected. However, in the case of depositing the copper on the entire inner surface of the via, in order to fill the inside of the via completely with copper with no remaining space, the deposition speed near the bottom surface of the via must be faster than the deposition speed at the opening part. If the speed of deposition near the bottom is the same as or slower than the speed of deposition at the opening end, the via might not be filled, or the opening might be closed before completion of the filling of the copper plating in the via, and empty spaces will remain inside, and neither of these cases is acceptable for practical use. Also, in the through hole plating, good covering strength in the through hole, which is called slowing power, is required.
Up to now, in order to promote the speed of deposition on near the bottom surface of via and the wall surface of the through hole, an electrolytic copper plating bath that includes a specific compound that contains sulfur has been used, and concerning the electrolysis conditions, generally direct current electrolysis that uses a soluble anode such as a sulfur-containing-copper anode, etc. was used. However in this method, although good via fill performance can be seen just after the bath is prepared, the electrolytic copper plating bath becomes unstable with the passing of time, and after a certain period of time, lumps are generated in the formation of the electrolytic copper plate layer, and the plate appearance becomes poor and the filling of the via becomes unstable, and these were the problems. Also, in through hole plating, the reliability for thermal impact and the slowing power used to be decreased.
In order to solve these problems, Kokai Patent No. 2002-249891 disclosed the electrolytic copper plating liquid which includes a specific compound that contains sulfur atoms, and a thiol reactive compound. As the thiol reactive compound, aliphatic, alicyclic, aromatic or hetero cyclic compound carboxylic acids, peroxo acids, aldehydes and ketones, and hydrogen peroxides are disclosed, and in the actual Examples, it described that formaldehyde can improve the filling ability. However, recently, the effects of formaldehyde on the environment and the human body have become a concern and also the ignition point of formaldehyde is low (66° C.), therefore, people have been searching for another compound which can improve the via fill ability and which can replace formaldehyde.